HUMIC SUBSTANCE FORMATION VIA THE OXIDATIVE WEATHERING OF COAL

Oxidative weathering of sedimentary organic matter in the Earth's surf icial environment is one of the major processes in the geochemical car bon cycle on geological time scales. It has been assumed in most geoch emical models that there is complete oxidation of sedimentary organic matter only to CO2. However, studies have shown that humic substances can be produced via the oxidation of coal. We have determined the aque ous oxidation kinetics of pyrite-free bituminous coal at 24 and 50 deg rees C by using a dual-cell flow-through method. At 24 degrees C, diss olved carbon is removed from the coal-water system mainly in the form of CO2 and is equivalent to 30-50% of the consumed oxygen. The remaini ng 50-70% of the consumed oxygen is retained on the coal surface in th e form of insoluble organic oxidation products. Formation of greater p roportions of dissolved organic oxidation products is expected under n atural conditions where water-rock contact time is much longer than in our experiments (18-25 h). FTIR analysis indicates marked increases i n carbonyl groups for coal oxidized in oxygenated water at 50 degrees C. Both dissolution of the solid oxidation products and the oxygen con sumption rate should be accelerated by an increase in pH.